As recent trends in the art, a semiconductor integrated circuit has been more and more highly integrated, and along with higher integration, the minimum pattern size reaches to the region of 100 nm or less. For the formation of fine patterns, lithography in which a resist material is exposed to ultraviolet light, has been conventionally used, and currently immersion lithography has attracted attentions as a new technology using ArF (fluorinated argon) excimer laser (wavelength of 193 nm), which has been developed for practical use, following the lithography.
In the immersion lithography a space between a projection lens of a stepper and a processing surface (wafer etc.) is filled with a medium having a larger refractive index than that of air, and as a result resolution is improved. In recent years, the techniques and materials, especially exposure devices and mediums (immersion mediums), for the immersion lithography have been developed.
However, there are problems typical for the immersion lithography such that various contaminations are eluted from a resist film to the immersion medium, as the resist film is exposed to the immersion medium (generally water) that fills the space between the projection lens and the processing surface. As a result of this, an optical element or inside of the exposure device is polluted, causing lower resolution due to exposure failure, or operational errors of the device.
To solve this problem, the method for forming a resist cover film on the top surface of the resist film has been considered. However, as the ArF excimer laser having a wavelength of 193 nm or F2 excimer laser that has a shorter wavelength (157 nm) than that of the ArF excimer laser is not passed trough general organic materials, the range of the selection of the materials usable for the resist cover film is extremely narrow.
Currently a resist cover film using a fluororesin has been known (see Japanese Patent Application Laid-Open (JP-A) No. 2006-301524), but various problems have been found on the resist cover film, such as insufficient effect for suppressing the interaction to the exposure medium (resist film), or elution of contaminations from the resist cover film, and mixing with the resist film.
Moreover, even if a resist cover film which solves such problems is developed, a step for forming another film (a resist cover film) is still necessary after the formation of a resist film. Therefore, it is clear that the use of the resist cover film itself becomes demerit in terms of throughput.
Note that, in recent years, a method for improving an acryl resin itself for using a resist material has been considered. However, the changing the resin structure requires a large change in the ability of the resist material to form a fine pattern. Therefore, it may take a considerable time to realize such the resin.
Moreover, the technique in which silsesquioxane resin is used as a resist material, and the generation of organic gas (out gassing) from the resist film is suppressed so as to prevent pollution within an exposure device (see International Publication No. WO 2004/076535). However, the silsesquioxane resin disclosed in this patent literature always contains a fluorine atom, which is known as having a low refractive index. As the technique of immersion lithography aims at improving the resolution by achieving the high refractive index, it is necessary for the resist material for exclude a fluorine atom which may cause lowering of the refractive index.
Accordingly it is a current situation that a material which does not lower the throughput in the production process of a semiconductor, is capable of suppressing the generation of pollution to an optical element or within an exposure device by suppressing the elution to an immersion medium, does not lose original function for a resist, and suitably used for a resist film which can be highly accurately exposed by immersion lithography and associated techniques thereof have not been developed, and it has been desired in the art to develop such techniques.